Microchannel plate and method of making the microchannel plate with an electron backscatter layer to amplify first strike electrons

ABSTRACT

A night vision system along with an image intensifier tube having a microchannel plate and method of forming the microchannel plate are provided. The microchannel plate comprises a plurality of spaced channels extending through the microchannel plate, wherein each channel sidewall surface near the input face of the microchannel plate comprises a series of layers formed thereon. The input face of the microchannel plate, as well as the sidewall surfaces of each channel near the input surfaces, are configured with an electron backscatter layer arranged between a contact metal layer and a secondary electron booster layer. When formed partially into the channel openings near the input face, the electron backscatter layer and overlying secondary electron booster layer are configured circumferentially around the sidewall surfaces and extend radially inward toward a central axis of each channel.

FIELD OF THE INVENTION

Example embodiments in general relate to night vision systems and, moreparticularly, image intensifier tubes and a method of manufacturing suchtubes with an improved microchannel plate (MCP). The MCP is configuredwith channel openings having an electron backscatter layer formed alongthe side of each channel opening between a metal contact layer and asecondary electron booster layer to scatter primary electrons onto thebooster layer and amplify resulting first strike electrons.

BACKGROUND

Night vision system such as night vision goggles typically include animage intensifier tube. The image intensifier tube, or “imageintensifier”, can include an electron multiplier arranged between aphotocathode and a sensor anode. The photocathode detects light in theform of photons sent through a lens from an object. The photoelectrons,or “electrons”, emitted from the photocathode are intensified oramplified. The amplified electrons can be drawn to the anode, where theycan be converted back to photons displayed on a screen. The anode orscreen can include a sensor that, upon receiving the increased ormultiplied number of electrons, senses those electrons and produces anintensified representation of the image on the screen. The photocathode,the electron multiplier, and the anode are typically supported in avacuum housing with gaps between the photocathode, electron multiplier,and the sensor anode to provide gain and facilitate the flow ofelectrons therebetween. The night vision system can further include oneor more eyepieces arranged on a night vision system, between the screenand the user's eyes.

One type of electron multiplier is a microchannel plate (MCP). The MCPis placed between the photocathode and a phosphor-covered sensor anode.The photocathode produces a pattern of electrons that correspond withthe pattern of photons produced from a low-light level image. Throughuse of electrostatic fields, the pattern of photoelectrons emitted fromthe photocathode are directed to the surface of the MCP. The MCP inputsurface, or input face, is substantially planar with openings spacedacross the input surface, and each opening extends as micro channels or“channels” that extend from the input surface to an opposed outputsurface substantially parallel to the input surface. As the incomingelectrons from the photocathode strike the inner surface of the channelopening at the input surface, secondary electrons are produced.Accordingly, the MCP emits from its micro channels a proportional numberof secondary emission electrons dependent on the primary electrons sentfrom the photocathode. The secondary emission electrons thereby form anelectron shower to amplify the electrons produced by the photocathode inresponse to the initial low-light level image. The shower of electrons,at an intensity much above that produced by the photocathode, are thendirected onto a phosphorescent screen of a phosphor-covered anode. Thephosphor layer on the screen produces an image of visible light thatreplicates the low-light level image as presented on the eyepiece of thenight vision system.

The MCP is typically formed from a bundle of very small cylindricaltubes, or glass fibers, which have been fused together into a parallelorientation. The bundle can then be sliced to form the MCP. The glassfibers of the bundle thus have their lengths arranged generally alongthe thickness of the MCP. An MCP may therefor contain an extremely largenumber of hollow tubes, or channels, between the input and output facesof the MCP. Each channel can form the electron passageway between theinput and output faces of the MCP.

In many instances, each tube is slightly angulated with respect to thenormal of the MCP planar input and output faces. For example, thecentral axis of each channel can be biased at a channel bias angle (CBA)relative to the normal of the MCP input and output planar surfaces andthe CBA can be between 5° to possibly 16° from normal. The CBA ensuresthat electrons which enter the channel normal to the MCP input face willstrike a channel wall. The CBA helps keep positive ions generated duringthe operation of the image intensifier from traveling to thephotocathode where they can cause damage. The physical properties of thechannel walls or radial sides are such that, generally, a plurality ofelectrons are emitted each time the sides are contacted by one energeticelectron. The material of the channel sidewall surfaces that curvearound the central axis of the channel have a high coefficient ofsecondary electron emission greater than one. Typically, the sidewallsurface of the channel is the glass cladding of each glass fiber afterthe core is removed. The glass sidewall surface itself has a relativelyhigh coefficient of secondary electron emission. The voltage bias acrossthe MCP is arranged such that the electron impacts lead to secondaryemission ratio greater than one. A material with a high secondaryelectron emission coefficient can be deposited onto the glass sidewallsurface to yield a secondary emission ratio greater than one.

At the input and output faces of the MCP is a contiguous metal contact.An input metal contact on the input face of the MCP is preferably biasedto a different voltage than the output metal contact on the output faceof the MCP. The contact metal applied to the input surface face is oftenreferred to as an input electrode, whereas the contact metal appliedacross the output surface face is often referred to as an outputelectrode. A portion of the contact metal at the output surface face canpenetrate into the MCP channels in order to collimate the outputelectron beam, and such result is generally known as output endspoilingto increase the resolution capabilities of the proximity output toward aphosphor-covered screen anode. The input and output electrodes arebiased to produce an electric field through each channel to draw thesecondary electrons produced at input channel openings through the MCPand toward the anode. The electrostatic field allows the secondaryelectrons to gain energy before the next impact with the MCP channelwall. This energy then allows more secondary electrons to be createdwhen the “parent” electron strikes the wall, and the resulting secondaryelectrons continue to increase, or cascade, along the length of eachchannel leading to the cascade effect. The cascaded electrons exit theindividual channels of the MCP under the influence of anotherelectrostatic field to further accelerate the multiplied electrons ontothe proximally placed phosphor-covered screen anode. The number ofelectrons emitted from the channel will average with those emitted fromthe other channels to produce an overall amplification or gain of theMCP.

The electrons which strike the MCP input face at the input face channelopenings from the photocathode are referred to as “primary electrons.”When the primary electrons strike the MCP for the very first time theycreate a group of secondary electrons referred to as “first strikeelectrons.” The first strike electrons can contain secondary electronscreated at the initial impact of the primary electron, and it can alsocontain secondary electrons created when the primary electron isbackscattered from within the MCP channel sidewalls and exits thesidewall back into the channel. This latter group of first strikeelectrons may contain the initial primary electron that is nowdesignated as a first strike electron because it may beindistinguishable from the secondary electrons.

The signal to-noise ratio (SNR) is a performance metric for imageintensifiers. The greater the SNR of an image intensifier, the greaterits low-light sensitivity and performance. The first strike efficiencyof the MCP component of the image intensifier helps determine the SNR.As the first strike efficiency is increased, so is the SNR.

A deficiency associated with conventional MCPs is the less than idealfirst strike efficiency at the input surface of the MCP. First, there isthe impact on the flat area between the channels which is a result ofthe less than 100% open area ratio (OAR) of the MCP. This loss can onlybe minimized by increasing the OAR. Second, the channel openings at theinput surface of the MCP are typically covered with contact metal neededto generate the electrostatic field. The input contact metal electrodehas a poor secondary emission coefficient, or ratio, compared to the MCPmaterial deeper in the channel. Typically, the contact metal extendingcontinuously across the input face and partially into the input channelopenings has a secondary emission coefficient less than one. Primaryelectrons striking the input contact metal suffer a reduction in theresulting first strike efficiency by reducing the number of first strikeelectrons generated from the input contact metal. To minimize thiseffect the metal coverage at the input openings is typically minimizedas much as possible.

It would be desirable to increase the immediate amplification of theelectrons striking the input channel openings, and thus increase thenumber of first strike electrons early on in each MCP channel. In turn,it would also be desirable to increase the first strike efficiency andthe amount of electron gain or amplification of the MCP without adverseeffects on the voltage bias efficiency of the contact metal on the inputand output plate surfaces extending into the input and output channelopenings.

SUMMARY

These and other objectives are achieved by a night vision system havingan improved MCP, and further having an improved method of manufacturingthe same. Each channel opening, preferably the input channel openingthat exists at the input face of the MCP, is either angulated into afunnel shape, or has a straight non-tapered input sidewall surface. Thesidewall surface at the input channel opening is advantageouslyconfigured so that a greater number of first strike electrons can beproduced each time a primary electron strikes a sidewall surface of thepresent, multi-layered sidewall surface of the input channel opening.Specifically, coating the sidewall surface that receives the primaryelectrons from the photocathode with multiple layers, one of which is anelectron backscatter layer, increases the number of first strikeelectrons yielded from each channel opening of the MCP.

An increase in first strike electrons increases the first strikeefficiency of the MCP, and decreases the number of secondary electronsneeded to be produced further down the channel to maintain the gain. TheMCP degrades the SNR of an image intensifier from the loss of electronsto the input contact metal electrode (i.e., endspoiling) at the flatarea between channels and the area at which the contact metal electrodeextends into the channel. The MCP also degrades the SNR from themultiplication statistics as electrons are multiplied through thechannel. This degradation of the SNR is the noise figure of the MCP andis defined as ratio of the SNR out of the MCP and the SNR input to theMCP. As the cascade of electrons continue down the channel, themultiplication events increase variation. For a given MCP output fluxvs. input flux (i.e., gain), increasing the first strike electronsgenerated from the primary electrons reduces the noise of the MCP byreducing the variation that increases during the cascade. The moremultiplication that occurs early in the channel the less variation thatis added from later multiplication events.

The electron backscatter layer is preferably formed over the contactmetal to direct or “backscatter” primary electrons that would normallycontact the relatively low secondary emission coefficient contact metal.Backscattering the primary electrons from the contact metal to anoverlying secondary electron booster layer will therefore increase thefirst strike electrons in the booster layer rather than decrease thefirst strike electrons if the electron backscatter layer were notpresent. It is therefore the successive arrangement of contact metal onthe input channel openings sidewall surface and on the input facebetween input channel openings, followed by an electron backscatterlayer on the contact metal layer, and further followed by a secondaryelectron booster layer on the electron backscatter layer that increasesimmediate amplification of the backscattered electrons. The successivearrangement produces more immediate production of first strike electronsthat increases first strike efficiency, amplification and gain of theMCP.

In accordance with at least one example of the present disclosure, anight vision system is provided. The night vision system can include animage intensifier tube placed between a lens and an eyepiece. The imageintensifier tube can include a photocathode, a phosphor covered anode,and a MCP arranged a spaced distance between the photocathode and thephosphor covered anode. The MCP can include a spaced plurality ofchannel openings. The channel openings on the input face of the MCP areoften referred to as the input channel openings. The channel openings onthe output face of the MCP can be referred to as output channelopenings. The output channel openings extend into the MCP and adjoincollinear with the input channel openings, so that each channel extendsentirely through the MCP. Each of the channel openings at the input faceof the MCP, sometimes referred to as “channel openings” for brevity, canbe configured with an electron backscatter layer configured between acontact metal layer and a secondary electron booster layer. Thecombination of secondary electron booster layer placed onto an electronbackscatter layer placed onto a contact metal layer forms a multilayerarrangement that extends at least partially circumferentially around asidewall surface of each of the channel openings.

The contact metal is an electrode coupled to a voltage supply togenerate an electric field through each of the channel openings from theinput face to the output face of the MCP. The electron backscatter layerand the secondary electron booster layer are formed in succession on theinput face as well as partially into each channel opening apredetermined distance from the input face. The electron backscatterlayer and secondary electron booster layer are formed in succession onthe contact metal, or contact metal electrode, and the predetermineddistance is approximately greater than the standard one half channeldiameter depth of the standard endspoiling material.

In accordance with another example of the present disclosure, a MCPwithin the image intensifier tube is provided. The MCP preferablycomprises a channel having a central axis extending at a CBA relative toan input face of the MCP. A first strike angle (FSA) at which theprimary electrons enter the channel openings near the input face istypically perpendicular or normal to the substantially planar inputface. The CBA is typically at an acute angle relative to the FSA so theprimary electrons can strike a “showered” sidewall surface of each ofthe channel openings near the input face. A first portion of the channelnear the input face, or input channel opening, comprises a glasssidewall surface. The contact metal layer is configured adjacent to andradially inward from the glass sidewall surface. The contact metal layeris thereafter coupled to a bias voltage to generate an electrostaticfield for energizing and drawing electrons down each channel. Anelectron backscatter layer is configured adjacent to and radially inwardfrom the contact metal layer. The electron backscatter layer isconfigured to receive primary electrons emitted from a photocathode andbackscatter those primary electrons in a somewhat opposite angulardirection from a surface of the electron backscatter layer. A secondaryelectron booster layer is configured adjacent to and radially inwardfrom the contact metal layer. The electron backscatter layer isconfigured to therefore receive primary electrons emitted from aphotocathode and backscatter those primary electrons from a surface ofthe electron backscatter layer. The secondary electron booster layer isconfigured adjacent to and radially inward from the electron backscatterlayer. The electron backscatter layer receives primary electrons emittedfrom a photocathode and backscatter those primary electrons from asurface of the electron backscatter layer. The secondary electronbooster layer receives primary electrons on its surface as well asbackscattered primary electrons from the surface of the electronbackscatter layer and to multiply the received and backscattered primaryelectrons.

The electron backscatter layer and the secondary electron booster layerare configured on only the input face of the microchannel plate betweenopenings and on the glass sidewall surface of the spaced channelopenings at the input face. Preferably, the electron backscatter layerand the secondary electron booster layer are configured on the contactmetal that was previously placed on the input face and partially downthe glass sidewall surface of the plurality of spaced input channelopenings. Preferably, the electron backscatter layer comprises anelement having an atomic mass unit (AMU) greater than 100 grams/mole,and preferably greater than 150 grams/mole. The secondary electronbooster layer preferably comprises Al₂O₃ or MgO formed or grown to athickness of approximately 30-50 Angstroms (Å). The secondary electronbooster layer can also comprise CsI, or other alkali halide materialhaving a high secondary emission ratio of preferably much greaterthan 1. The contact metal can comprise multiple layers if, for example,the electron backscatter layer requires an additional layer for reliableadhesion thereto. The contact metal layer or layers preferably compriseInconel or Nichrome. While contact metal should preferably have goodconductive capability, its secondary emission ratio is typically lessthan 0.8 and, instead of generating secondary electrons, contact metaltypically absorbs electrons rather than producing them. Thus, contactmetal produces no substantial amount of first strike electrons, oramplification thereof. Accordingly, the contact metal is advantageouslycovered with an electron backscatter layer that backscatters the primaryelectron onto the secondary electron booster layer with a high secondaryemission ratio much greater than 1.0. The contact metal has minimalbackscatter capability since it has an AMU less than 60. If the electronbackscatter layer is not present, the contact metal cannot by itselfbackscatter a sufficient number of primary electrons onto the secondaryelectron booster layer to increase first strike efficiency.

In accordance with yet another example of the present disclosure, amethod is provided for making an MCP. The method includes forming glasscores surrounded by respective glass cladding at a first angle relativeto opposing input and output faces of the MCP plate. The glass cores arethen etched to remove the cores entirely from the remaining glasscladding leaving a plurality of spaced channels. A contact metal layeris then formed on both opposing input and output faces of the plate andpartially into each of the spaced channels. An electron backscatterlayer is then formed on the contact metal on the input face, andpreferably not on the output face. The electron backscatter layer isformed on the input face and contiguously only partially into each ofthe spaced channels near only the input face. A secondary electronbooster layer is then formed on the electron backscatter layer on theinput face and contiguously only partially into each of the spacedchannels near the input face. The contact metal is then coupled to abias voltage to electrostatically draw the first strike electrons fromthe secondary electron booster layer. A portion of the secondaryelectrons is produced from primary electrons that are backscattered fromthe electron backscatter layer. The glass cladding at the boundarybetween the glass cores and the surrounding glass cladding can be etchedprior to etching the glass cores to remove the cores entirely. Byetching the glass cladding at the boundary, and subsequently etching theglass cores to remove the cores entirely, produces a funnel shapedopening into each of the channel openings. The electron backscatterlayer is preferably formed to a thickness typically greater than but notlimited to 30 Å, and more preferably between 30 Å to 50 Å.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present disclosure are best understood from thefollowing detailed description when read in connection with theaccompanying drawings. According to common practice, the variousfeatures of the drawings are not drawn to scale, or are only shown inpartial perspective. The dimension of the various embodiments are shownarbitrarily expanded or reduced for clarity. Like numerals are used torepresent like elements among the drawings. Included in the drawings arethe following features and elements, and reference will now be made toeach drawing in which:

FIG. 1 is a partial block diagram of a night vision system utilizing animage intensifier tube having a MCP;

FIG. 2 is a partial top view of a MCP along section 2-2 of FIG. 1 ;

FIG. 3 is a partial cross sectional view along section 3-3 of FIG. 2 ,showing each channel central axis aligned at a CBA and a FSA at whichthe primary electrons strike the showered sidewall surface of eachchannel wall near each channel opening at the input face of the MCP;

FIG. 4 is a partial cross sectional view of a single channel opening atthe input face of the MCP having an electron backscatter layer arrangedbetween a contact metal layer and a secondary electron booster layer;

FIG. 5 is an expanded cross sectional view along region 5 of FIG. 4showing amplified first strike electrons generated from primaryelectrons striking the secondary electron booster layer from primaryelectrons backscattered from the electron backscatter layer; and

FIG. 6 is a flow diagram of a method for forming a MCP having channelopenings with an electron backscatter layer formed between a contactmetal layer and a secondary electron booster layer along a sidewallsurface of each channel opening to produce backscattered primaryelectrons as well as and first strike electrons from the backscatteredprimary electrons.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The following discussion is directed to various example embodiments.However, one of ordinary skill in the art will understand that theexamples disclosed herein have broad application, and that thediscussion of any embodiment is meant only to be exemplary of thatembodiment, and not intended to suggest that the scope of thedisclosure, including the claims, is limited to that embodiment.

As noted above, the drawing figures are not necessarily to scale.Certain features and components herein may be shown exaggerated in scaleor in somewhat schematic form and some details of conventional elementsmay not be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . . ” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection of the two devices,or through an indirect connection that is established via other devices,components, nodes, and connections. In addition, as used herein, theterms “axial” and “axially” generally mean along or parallel to a givenaxis (e.g., x, y or z direction or central axis of a body, opening,channel, outlet or port), while the terms “radial” and “radially”generally mean perpendicular to the given axis. For instance, an axialdistance refers to a distance measured along a central axis, and aradial distance means a distance measured perpendicular to the centralaxis. Radially opposite can mean on opposite sides of the central axisand in an arcuate pattern only partially around and spaced an axialdistance from the central axis.

Referring now to FIG. 1 , a partial block diagram of a night visionsystem 12 is shown. Night vision system 12 comprises an imageintensifier tube 14 placed between a pair of lenses 16 and 18. Lens 16can be a focusing lens that focuses photons from object 15 onto imageintensifier 14. Lens 18 can be an eyepiece that directs the outgoingphotons produced from image intensifier 14 onto a user's eye. The nightvision system 12 can be, for example, goggles, where eyepiece 18 caninclude two eyepieces.

Image intensifier 14 can be a vacuum tube and is fairly well known,based on Generation-III (GaAs photocathode) or Generation-II(multi-alkali photocathode) image intensifier tube. Within the imageintensifier tube 14 is a photocathode 20. Photocathode 20 may comprise afaceplate made of glass and coated with GaAs on a backside surface ofthe faceplate. Other type III-V materials can be used such as GaP, GaIn,AsP, InAsP, InGaAs, etc. Alternatively, photocathode 20 may be known asBi-alkali photocathode. Photoemissive semiconductor material ofphotocathode 20 absorbs photons arriving on a photon receiving face ofimage intensifier tube 14. Photons absorb by photocathode 20 cause thecarrier density of the semiconductor material to increase, therebycausing the material to generate a photocurrent of electrons 21 emittedfrom the backside electron emission face of photocathode 20.

Photocathode 20, according to one example, converts non-visible orvisible low light sources. The non-visible light sources can be nearinfrared or short wave infrared to visible. An electron multiplier 22receives electrons 21, and multiplies those electrons to producemultiplied electrons 23. A popular electron multiplier includes a MCP.MCP 22 is typically provided through a plurality of glass fibers, eachhaving a core surrounded by an exterior glass cladding. Each of theplurality of cores can be removed, leaving a spaced plurality ofmicrochannels, or “channels” from the input face to the output face ofthe MCP. The inside walls or sides of each channel opening has a highelectron emissivity coefficient to produce a shower of secondaryelectrons. The channels are spaced from each other and extend from theinput planar surface, or input face, to the output planar surface, oroutput face, where multiplied electrons are emitted. The secondaryemission electrons amplify the electrons produced by the photocathode inresponse to initial low-light level images. The shower of electrons areproduced at an intensity greater than that produced by the photocathode,and therefore the MCP 22 has amplification and gain. Voltage sources canbe applied between the various elements of image intensifier 14 to drawelectrons from photocathode 20 to MCP 22, through MCP 22, and from thebackside emissions surface of MCP 22 onto anode 24. The voltage sourcesproduce an electrostatic field that draws both primary and secondaryelectrons through image intensifier 14 to impart the desired energy tothe multiplied electrons applied to the phosphor covered screen, oranode 24. The phosphor-covered screen converts the multiplied electronpattern initiated from photocathode 20 to a visible light image of theinitially received low level image from target 15. The emitted photonsare directed by optics, such as a fiber optic bundle of anode 24 fromimage intensifier 14 onto eyepiece 18. When viewing through eyepiece 18,a user can discern low level visible or non-visible photons reflected orgenerated from target image 15 through use of the amplified gain andelectron multiplication of MCP 22.

Turning now to FIG. 2 , a top view is illustrated when viewed fromphotocathode 20 of MCP 22. Specifically, the top view along section 2-2of FIG. 1 is illustrated. A plurality of channels extend entirely thoughMCP 22. Each channel 26 is an opening from the electron input face tothe multiplied output face of the MCP 22. Since MCP 22 is shown in FIG.2 from the photocathode side, the input face is therefore the electronreceiving side that receives primary electrons 21 from photocathode 20,as shown in FIG. 1 . Each channel 26, along with the input and outputopenings thereof is preferably the same diameter among channels andopenings. In other words, the channel 26 dimensions in FIG. 3 arepreferably consistent across MCP 22. The pitch or spacing betweenchannels 26 should also be consistent. It is desirable that the ratio ofopening area to the space between openings have an open area ratio (OAR)as high as possible. The channel openings on the input side of the MCPcan be funnel shaped to increase the OAR greater than 70% whilemaintaining proper distances for structural integrity between sidewallsurfaces below the funnel opening.

Turning now to FIG. 3 , a cross-sectional view of plane 3-3 of FIG. 2 isshown. FIG. 3 illustrates in more detail the plurality of channels 26within the honeycomb structure of MCP 22. The channels provide a fairlyreliable electron multiplier provided the channels 26 are properlyslanted or biased at an optimal CBA. An electric field is createdbetween the voltage source V_(s) supplied to contact metal 30 appliedcontinuously across the input face and contact metal 32 appliedcontinuously across the output face. The channels 26 are the openingsthat therefore exist between the input and output faces of MCP 22, thosechannel sidewall surfaces are preferably scrubbed to remove anyremaining impurities that could inhibit secondary emissions or producepositive ion bombardment of the photocathode. The electron-acceleratingelectrostatic fields through each channel 26 occur by applying contactmetal on the input and output faces and biasing the contact metal withthe voltage supply V_(s), wherein the contact metal can include a goodconductive material such as Inconel or Nichrome. Contact metal 30 and 32can extend partially into the channel. The slant angle, or CBA, is takenalong the central axis of the channels 26 and is substantially identicalacross each channel 26 since the channels are parallel to one another.The CBA can be between 5° and 16° relative to the normal of themicrochannel plate planar input face.

The electrons 21 sent from photocathode 20 (FIG. 1 ) strike a visibleside of each channel 26 at a first strike angle (FSA). The visible sideis the sidewall surface of each channel that can be seen at a line ofsite normal to the input face of the MCP. That normal line of site isthe FSA noted in FIG. 3 . The electrons sent from photocathode 20 arehenceforth the primary electrons 21 directed along FSA that strike or“shower” the visible side, which can also be referred to as showeredside. The side of the channel substantially opposite the visible, orshowered, side of the channel is referred to as the shadowed side whereprimary electrons generally do not strike. Since secondary electrons aregenerated from the first strike of primary electrons 21, the secondaryelectrons resulting from the first strike are henceforth first strikeelectrons. The first strike electrons are only those produced from theprimary electrons strike. The first strike electrons include bothsecondary electrons as well as possibly the primary electron. Subsequentstrikes created from the produced secondary electrons further down eachchannel are sometimes referred to as secondary electron strikes (orsometimes referred to as tertiary electron strikes, etc.) but are notfirst strike electrons. The secondary electrons, either from the firststrike electrons or from subsequently created secondary strikeelectrons, are electrostatically biased down each channel 26 where evenfurther secondary strikes (or sometimes referred to as tertiary,quaternary, etc. strikes) occur on the opposing radial surfaces of thosechannels to further increase the cascading or multiplying effect. Whilemultiple strikes can occur from the input surface to the output surfaceof each channel, and multiplied electrons with gain can result, the veryfirst strike of only the primary electron 21 produces the first strikeelectrons 36, for brevity in illustration, produced from only onechannel. It is understood that each channel produces first strikeelectrons 36 from the first strike of primary electrons 21 at a firststrike angle FSA relative to the channel bias angle. The FSA is normalto the input face of the MCP 22. The FSA, while normal to the input faceof MCP 22, is at an acute angle relative to CBA. CBA is preferablybetween 5° and 16°, and more preferably between 5° and 8° relative tonormal, or FSA.

The overall electron multiplication/amplification, or gain, of MCP is inlarge part dependent on the mean number of electrons produced inresponse to an input event. Those electrons produced in response to aninput event, or first strike electrons 36 produced in response to aprimary electron 21 input event, will have significant impact on theoverall performance of the MCP 22. As will be noted below in referenceto FIG. 4 , one way to increase the production of first strike electrons36 is to apply secondary electron booster material with a high secondaryemission coefficient, or ratio, to the input side of the electronreceiving face to coat the inside channel walls down along the channelto a predetermined depth. Such booster material may be Al₂O₃, MgO, CsIor other alkali material, or any other material or materials in whichthere is compatibility with the processing equipment and other materialsused to manufacture the plate and the channels of MCP 22.

Turning now to FIG. 4 , a partial cross sectional view of a singlechannel 26 is shown. The single channel 26, like all the other channels26 within an MCP, comprise a glass cladding 40 having a sidewall surface42. The glass cladding 40 has an input surface 44 at the input face ofthe MCP 22. The sidewall surfaces 42 and the input surfaces 44 aretherefore made of glass material with a relatively high secondaryemission ratio much greater than 1.0. The sidewall and input surfaces 42and 44 can be prepared not only to remove any impurities from thoseglass surfaces but also to provide good adhesion for a contact metal 30placed on the input face of MCP 22 as well as partially into eachchannel 26 along sidewall surfaces 42. Contact metal 30 is deposited ina continuous, contiguous fashion on the surfaces 42 and 44, but onlypartially into channel 26 along surface 42.

Contact metal 30 is preferably deposited ½ D, where is D is the diameterof channel 26. However, it is understood that for zero endspoiling thedeposition distance can be less than ½ D, but for enhanced adhesion ofthe contact metal the deposition distance along the sidewall surface canbe slightly greater than ½ D. As noted in FIG. 4 , the dimensions arenot to scale and are modified to more clearly show certain features suchas the multi-layer features and the depths of their formation. As notedabove, the contact metal 30 is made of a good conductive material, suchas a Inconel or Nichrome. Contact metal 30 is deposited to a thicknessof approximately 1500 to 2500 Å on sidewall surfaces 42 and input facesurfaces 44. Contact metal 30 can be a single layer or multiple layers,and the effective depth of deposition into channel 26 along sidewallsurfaces 42 is a function of the geometry of the channel plate as wellas the angle of evaporation at which the evaporation tool appliescontact metal 30 onto the sidewall surfaces 42. The angle of evaporationis the angular displacement of the evaporation source used to applycontact metal 30 from the plate access or the channel 26 long axis, orcentral axis, as measured at the channel input openings. The angle ofevaporation, in combination with the geometry of the MCP and theevaporation source distanced from the MCP produces the desired depth ofcoverage down each channel along the sidewall surfaces 42. The angle ofevaporation can vary and is preferably parallel to the CBA, or at a moreacute angle than CBA. According to one example of deposition, the MCP 22or the evaporation source (not shown) can be rotated, or rotated along acircumferentially variable angle relative to the normal of the inputface. It is therefore necessary to coat the surfaces 42 and 44 of theglass with the contact metal 30 using various coating or evaporationmethodologies, including directional deposition methodologies coupledwith rotational or variable angulation of the deposition source and/orthe MCP 22. It is preferred that the coating along the sidewall surfaces42 may extend more than a ½ diameter D into channel 26.

An electron backscatter layer 48 is placed on and completely overcontact metal 30. By covering the entire contact metal 30, any primaryelectrons that impinge on the input face, or the sidewall surfaces ofchannel openings, having contact metal 30 will be directed away fromcontact metal 30. The primary electrons are directed by electronbackscatter layer 48 so as not to deleteriously affect the primaryelectron absorption that would normally take place in contact metal 30.While contact metal 30 is a fairly good conductor, it is a relativelypoor material for secondary electron emissivity. In some cases, but byno means all, only a single secondary electron may be ejected fromcontact metal layer 30 thereby producing no amplification ormultiplication of the initial electron strike, or primary electronstrike.

The electron backscatter layer 48 is made of a material or elementhaving a high atomic mass unit (AMU). Preferably, the AMU of electronbackscatter layer 48 is greater than 100 grams/mole, and more preferablygreater than 150 grams/mole. A preferred element used in electronbackscatter layer 48 is gold, having an AMU of approximately 196.Electron backscatter layer 48 is preferably deposited, evaporated, orgenerally formed to a thickness dependent on the accelerating voltageand is typically, but not limited to, thickness between 30 Å to 50 Å.Although electron backscatter layer 48 is conductive like contact metal30, the similarities stop at conductivity. Unlike the electronabsorption feature of contact metal 30, electron backscatter layer 48necessarily does not absorb electrons but instead reflects thoseelectrons or backscatters the electrons away from contact metal 30.Backscattering electrons from electron backscatter later 48 necessarilythen implies that these backscattered electrons will make a second passthrough the secondary electron booster layer 52.

Secondary electron booster layer 52 is deposited upon, adjacent to, andentirely over electron backscatter layer 48. Similar to electronbackscatter layer 48, secondary electron booster layer 52 can bedeposited or formed using similar formation tools and techniques used informing the previous layers. The secondary electron booster layer 52,similar to the previous layers, can consist of multiple layers formed toa thickness of approximately 30 to 50 Angstroms of a high secondaryemission material such as Al₂O₃ or MgO. Alternatively, secondaryelectron booster layer or layers 52 can consist of CsI along with otheralkali halide materials.

While the sidewall surfaces 42 of glass cladding 40 has a secondaryemission ratio that can exceed 1.0, the secondary electron booster layer52 can have a higher secondary emission coefficient, or ratio, than theglass cladding surface. For example, secondary electron booster layer 52can have a secondary emission ratio between 2.0 and 10.0. Accordingly,regardless of the secondary emission coefficient or ratio, secondaryelectron booster layer 52 preferably has a higher secondary emissivitythan then glass cladding itself.

Turning now to FIG. 5 , an expanded cross-sectional view along region 5of FIG. 4 is shown. In particular, FIG. 5 illustrates the functionalityof electron backscatter layer 48 placed between contact metal 30 andsecondary electron booster layer 52. Primary electron 21 is shownstriking the surface of secondary electron booster layer 52, andcorrespondingly emitting first strike electrons 36 therefrom. Apercentage of the primary electrons 21 will penetrate the secondaryelectron booster layer 52, generating backscattered electrons 56 offelectron backscatter layer 48. Thus, rather than being absorbed intocontact metal 30, where subsequent first strike electrons cannot beproduced therefrom, the backscattered electrons 56 reflect orbackscatter from the intermediately placed electron backscatter layer48. Backscattered electrons will then generate additional secondaryelectrons as they exit the secondary electron booster layer 52. Theadditional secondary electrons are therefore additional first strikeelectrons 36 a that, when added to the non-backscattered previous firststrike electrons 36, cumulatively add to the total number of firststrike electrons. An increase of the first strike efficiency of the MCP22 results. Increasing the number of first strike electrons provide anMCP first strike amplifier resulting in an improved performance yield ofthe MCP 22.

Turning now to FIG. 6 , a method is shown for forming an MCP havingchannel openings with an electron backscatter layer formed between acontact metal layer and a secondary electron booster layer along asidewall surface of each channel opening. The method begins by forming aplurality of glass cores each surrounded by glass cladding 62. Next theglass cores are removed using an etchant selective to the core material64. Alternatively, in step 64 a selective etch can be used to formfunnel shapes at the input and output faces of the channel. Regardlessof whether the resulting channel opening is a funnel shape or not, aplurality of microchannels or channels are formed entirely through theMCP at the culmination of steps 62 and 64.

Once the channels are formed, contact metal is deposited on the inputface of the MCP and partially within each channel along a sidewallsurface of each channel 66. The process of forming the contact metal caninvolve directional deposition or evaporation, or other techniques inwhich the contact metal is continuously and contiguously placed acrossthe entire input face as well as partially into each channel sidewallsurface. If the contact metal is optimally placed, there can exist noinput endspoiling. That formation process can involve directionaldeposition 68 as well as a spin 70 of the deposition tool or MCP.Alternatively, a rotating planetary deposition system can be used withsatellite heads on which one or more MCPs are placed at an angle to thesource evaporation tool to deposit the material to the desired depth asthe head experiences a full rotation.

Next, the electron backscatter layer is formed adjacent to, on, andentirely over the contact metal previously placed at step 72. Theelectron backscatter layer can be formed by directional deposition andspin techniques 74 and 70, respectively. Alternately, the directionaldeposition 74 can be an addition to, or the same as, the directionaldeposition 68 used in forming contact metal 66. Thereafter, thesecondary electron booster layer 76 is formed. Similar to the electronbackscatter layer and the contact metal layer, secondary electronbooster layer is formed on the input face and contiguously onlypartially into each of the spaced channels near only the input face. Thesecondary electron booster layer can be formed only partially into eachchannel, but can also be formed to cover as much as the entire channelcircumference lengthwise along the channel sidewall surface. Likewise,the secondary electron booster layer can be deposited directionally 78,and the MCP and/or the deposition tool can be spun during deposition 70.

Once the layers are formed in succession and on top of one another onthe input face between channels as well as partially into the sidewallsurfaces of each channel, the contact metal is coupled to a bias voltage80. It is noted that only two layers, the backscatter and electronbooster layers, can be used if the backscatter layer can adhere well tothe underlying glass cladding and serve as the contact metal. Thecontact metal layer is typically used as an adhesion layer having goodconductivity. If the electron backscatter layer were to have goodadhesion properties and is conductive with a high AMU, then the contactmetal layer can be eliminated and the deposition step involving contactmetal can be eliminated. This would leave only two layers, with thecontact metal layer eliminated entirely. The bias voltage draws firststrike electrons from the secondary electron booster layer as well as aportion of which are produced from primary electrons backscattering fromthe electron backscatter layer 82 and 84.

It is important to note that the construction and arrangement of thevarious example embodiments are illustrative only. Although only a fewembodiments have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein. Forexample, elements shown as integrally formed may be constructed ofmultiple parts or elements, the position of elements may be reversed orotherwise varied, and the nature or number of discrete elements orpositions may be altered or varied. The order or sequence of any processor method steps may be varied or re-sequenced according to alternativeembodiments. Additionally, features from particular embodiments may becombined with features from other embodiments as would be understood byone of ordinary skill in the art. Other substitutions, modifications,changes and omissions may also be made in the design, operatingconditions and arrangement of the various example embodiments withoutdeparting from the scope of the present invention.

As used herein, the terms “about,” “approximately,” substantially,”“generally,” and the like mean plus or minus 10% of the stated value orrange. In addition, as used herein, the singular forms “a,” “an” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. The term “and/or” includes any andall combinations of one or more of the associated listed items. Forexample, reference to “a feature” includes a plurality of such“features.” The term “and/or” used in the context of “X and/or Y” shouldbe interpreted as “X,” or “Y,” or “X and Y”.

The illustrated embodiments described in the detailed description,drawings, and claims are not meant to be limiting. Other embodiments maybe used, and other changes may be made, without departing from thespirit or scope of the subject matter presented herein. Additionally,particular aspects of each embodiment may also be used in conjunctionwith other embodiments of the present disclosure and thus, the disclosedembodiments may be combined as understood in the art. It will be readilyunderstood that the aspects of the present disclosure, as generallydescribed herein, and illustrated in the figures, can be arranged,substituted, combined, separated, and designed in a wide variety ofdifferent configurations, all of which are explicitly contemplatedherein.

It should be noted that any use of the term “example” herein to describevarious embodiments is intended to indicate that such embodiments arepossible examples, representations, and/or illustrations of possibleembodiments (and such term is not intended to connote that suchembodiments are necessarily extraordinary or superlative examples).Further, as utilized herein, the term “substantially” and similar termsare intended to have a broad meaning in harmony with the common andaccepted usage by those of ordinary skill in the art to which thesubject matter of this disclosure pertains. It should be understood bythose of skill in the art who review this disclosure that these termsare intended to allow a description of certain features described andclaimed without restricting the scope of these features to the precisenumerical ranges provided. Accordingly, these terms should beinterpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described and claimed(e.g., within plus or minus five percent of a given angle or othervalue) are considered to be within the scope of the invention as recitedin the appended claims. The term “approximately” when used with respectto values means plus or minus five percent of the associated value.

The terms “coupled” and the like as used herein mean the joining of twomembers directly or indirectly to one another. Such joining may bestationary (e.g., permanent) or moveable (e.g., removable orreleasable). Such joining may be achieved with the two members or thetwo members and any additional intermediate members being integrallyformed as a single unitary body with one another or with the two membersor the two members and any additional intermediate members beingattached to one another.

It should be noted that although the diagrams herein may show a specificorder and composition of method steps, it is understood that the orderof these steps may differ from what is depicted. For example, two ormore steps may be performed concurrently or with partial concurrence.Also, some method steps that are performed as discrete steps may becombined, steps being performed as a combined step may be separated intodiscrete steps, the sequence of certain processes may be reversed orotherwise varied, and the nature or number of discrete processes may bealtered or varied. The order or sequence of any element or apparatus maybe varied or substituted according to alternative embodiments.Accordingly, all such modifications are intended to be included withinthe scope of the present disclosure as defined in the appended claims.

Without further elaboration, it is believed that one skilled in the artcan use the preceding description to utilize the claimed inventions totheir fullest extent. The examples and embodiments disclosed herein areto be construed as merely illustrative and not a limitation of the scopeof the present disclosure in any way. It will be apparent to thosehaving skill in the art that changes may be made to the details of theabove-described embodiments without departing from the underlyingprinciples discussed. In other words, various modifications andimprovements of the embodiments specifically disclosed in thedescription above are within the scope of the appended claims. Forexample, any suitable combination of features of the various embodimentsdescribed is contemplated.

What is claimed is:
 1. A night vision system, comprising: an imageintensifier tube placed between a lens and an eyepiece, wherein theimage intensifier tube comprises: a photocathode; a phosphor coveredanode; a microchannel plate arranged a spaced distance between thephotocathode and the phosphor covered anode, wherein the microchannelplate comprises a spaced plurality of channel openings with an electronbackscatter layer configured between a contact metal layer and secondaryelectron booster layer circumferentially around a sidewall surface ofeach of the channel openings.
 2. The night vision system of claim 1,wherein the microchannel plate comprises an input face substantiallyplanar surface spaced from the photocathode and an opposing output facesubstantially planar surface spaced from the phosphor covered anode. 3.The night vision system of claim 2, wherein the contact metal is coupledto a voltage supply to generate an electric field through each of thechannel openings from the input face to the output face.
 4. The nightvision system of claim 2, wherein the contact metal layer, the electronbackscatter layer and the secondary electron booster layer are formed insuccession on the input face and on the sidewall surface of each of thechannel openings.
 5. The night vision system of claim 2, wherein theelectron backscatter layer and the secondary electron booster layer areformed in succession on only the input face and on the sidewall surfaceof each of the channel openings extending into the channel openings apredetermined distance from the input face.
 6. The night vision systemof claim 2, wherein the electron backscatter layer and the secondaryelectron booster layer are formed in succession on the sidewall surfaceof each of the channel openings with the electron backscatter layerextending into the channel openings a predetermined distance from theinput face a distance equal to or less than the secondary electronbooster layer.
 7. The night vision system of claim 5, wherein thepredetermined distance is approximately one half a diameter of each ofthe channel openings.
 8. The night vision system of claim 1, wherein thecontact metal layer, the electron backscatter layer and the secondaryelectron booster layer are formed in succession radially inward from thesidewall surface circumferentially around an entirety of the sidewallsurface a distance approximately one half the diameter of each of thechannel openings along the sidewall surface from an input face of themicrochannel plate.
 9. The night vision system of claim 1, wherein theelectron backscatter layer comprises an element having an atomic massunit greater than 100 grams/mole, and more preferably greater than 150grams/mole.
 10. A microchannel plate comprising: a channel having acentral axis extending at a channel bias angle relative to an input faceof the microchannel plate; a first portion of the channel near the inputface comprising: a circumferentially extending glass sidewall surface; acontact metal layer coupled to a bias voltage, wherein the contact metallayer is configured adjacent to and radially inward from the glasssidewall surface; an electron backscatter layer configured adjacent toand radially inward from the contact metal layer, wherein the electronbackscatter layer is configured to receive primary electrons emittedfrom a photocathode and backscatter the primary electrons from a surfaceof the electron backscatter layer; a secondary electron booster layerconfigured adjacent to and radially inward from the electron backscatterlayer, wherein the secondary electron booster layer is configured toreceive the backscattered primary electrons from the surface of theelectron backscatter layer and to multiply the received backscatteredprimary electrons.
 11. The microchannel plate of claim 10, wherein theelectron backscatter layer and the secondary electron booster layer areconfigured on only the input face of the microchannel plate and on theglass sidewall surface of a plurality of channels adjacent to the inputface.
 12. The microchannel plate of claim 10, wherein the electronbackscatter layer and the secondary electron booster layer areconfigured along the input face and along the glass sidewall surface ofeach of a plurality of channels a predetermined distance from the inputface.
 13. The microchannel plate of claim 10, wherein the predetermineddistance is greater than one half a diameter of one of the plurality ofchannels.
 14. The microchannel plate of claim 1, wherein the electronbackscatter layer comprises an element having an atomic mass unitgreater than 100 grams/mole, and more preferably greater than 150grams/mole.
 15. The microchannel plate of claim 1, wherein the electronbackscatter layer comprises a thickness of between 30 Å to 50 Å.
 16. Amethod of making a microchannel plate, comprising: forming glass coressurrounded by respective glass cladding at a first angle relative toopposing input and output faces of a plate; etching the glass cores toremove the cores entirely from the remaining glass cladding leaving aplurality of spaced channels; forming a contact metal layer on bothopposing input and output faces of the plate and partially into each ofthe spaced channels; forming an electron backscatter layer on thecontact metal on the input face and contiguously only partially intoeach of the spaced channel near only the input face; forming a secondaryelectron booster layer on the electron backscatter layer on the inputface and contiguously only partially into each of the spaced channelsnear only the input face; and coupling the contact metal to a biasvoltage to draw first strike electrons from the secondary electronbooster layer, a portion of which are produced from primary electronsbackscattering from the electron backscatter layer.
 17. The method ofclaim 16, further comprises etching the glass cladding at the boundarybetween the glass cores and the surrounding glass cladding prior toetching the glass cores to remove the cores entirely.
 18. The method ofclaim 17, wherein etching the glass cladding at the boundary andsubsequently etching the glass cores to remove the cores entirelyproduces a funnel shaped opening into each of the spaced channels. 19.The method of claim 16, wherein forming the electron backscatter layercomprises directionally depositing an element having an atomic mass unitgreater than 100 grams/mole, and more preferably greater than 150grams/mole.
 20. The method of claim 16, wherein forming the electronbackscatter layer to a thickness of between 30 Å to 50 Å.